Conventionally, a plate material such as a plaster board is fixed to a ceiling or to a wall by screw driving. A screw driver is a power tool for performing this screw driving. Japanese Examined Patent Application Publication No. H3-5952 discloses a screw driver including a motor and an end bit driven by the motor for driving a screw. The screw driver further includes a first clutch element, an intermediate clutch, and a second clutch element in this order between the motor and the end bit. With the screw driver, cam threads on the first clutch element located at the motor side engage motor-side cam threads on the intermediate clutch to rotate the intermediate clutch, and an engagement member of the intermediate clutch further rotates the second clutch element.